The present invention relates to a hot standby communications system for enhancing the reliability of microwave communications or the like.
Approaches heretofore proposed to promote reliable microwave communications include a hot standby communications system which uses regular equipment and back-up equipment. The system is arranged such that both the regular and back-up equipment systems are constantly ready to receive input power and, when the regular equipment fails, the back-up system replaces it to avoid service interruption.
In a hot standby communications system of the kind described, where a received input is applied to the regular equipment but not to the back-up equipment, it is difficult to detect failures which might occur in the back-up equipment and, therefore, to realize the higher reliability afforded by a parallel redundant construction. In light of this, a construction which feeds a part of a received input to the standby back-up equipment is often employed. This, as it solves the abovementioned problem in, brings about another problem that the received input applied to the regular equipment is cut down complementarily to the fraction which is applied to the back-up equipment, resulting in a deterioration in communications quality. For example, where a received input is divided into two equal parts so as to distribute one to the regular equipment and the other to the back-up equipment, power is undesirably reduced complementarily to lower the received input by 3 dB at both the regular and back-up systems.
The above situation may be coped with by first giving priority to the communications quality of the regular equipment at, as has also been proposed. Specifically, the improvement is achievable by splitting the received input into signals having two different values of powers, and routing the greater one of them to the regular equipment and the smaller one to the back-up. This prior art branching scheme, however, cannot avoid the drawback that once the initial regular equipment fails, the greater power distributed thereto translates into a greater fall in the communications quality of the back-up equipment which continues until the former is repaired.